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Carbon Monoxide reading on ground


Adi

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Hey folks,

Went to try and fly last Thursday in my J, and when I got to the runup area I started hearing a faint beep - my carbon monoxide sensor was alerting and showing readings in the 80s. Strangely this was before I actually started my run-up, and the reading would be high with the door closed, but when opening the door it would go back to around 7. Also after leaving the run-up area the reading went back to around 7 with the door closed. Hard to explain - there were no other planes in the run-up area..

I didn't end up flying and am having a mechanic on the field look at it on Tuesday. 

Wanted to poll this group in case y'all had a similar experience, would be curious to learn what the defect was and how you got it fixed.

Adi

 

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9 minutes ago, Adi said:

Hey folks,

Went to try and fly last Thursday in my J, and when I got to the runup area I started hearing a faint beep - my carbon monoxide sensor was alerting and showing readings in the 80s. Strangely this was before I actually started my run-up, and the reading would be high with the door closed, but when opening the door it would go back to around 7. Also after leaving the run-up area the reading went back to around 7 with the door closed. Hard to explain - there were no other planes in the run-up area..

I didn't end up flying and am having a mechanic on the field look at it on Tuesday. 

Wanted to poll this group in case y'all had a similar experience, would be curious to learn what the defect was and how you got it fixed.

Adi

 

Was their another aircraft performing a runup in the runup area?  Were your wemac or overhead vents open?

I found a ripped SCAT tube going to the muffler when I noticed a rise in a CO on the ground- I think it’s best to have it looked over, just like you’re doing.

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Good decision not to fly until you find out more. Start by checking the exhaust system for signs of leaks.

Depending on the sensitivity of the sensor, a repeatable change from 7ppm with doors open to 80 ppm with doors closed would keep me from flying. The most I sometimes see is 10 to 20 ppm in my J, and only during taxi. In flight the max is typically below 10ppm.

Stay safe - Hank


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While flying, the cabin has negative pressure all around it. The air goes in the vents and out all the cracks and voids. While on the ground, you have the exhaust coming out the tail pipe. It can be blown by the wind just about anywhere. there are lots of places it can get in.

When the plane was new the factory taped up all the cracks and crevice's. over the years this tape along with your rudder, Johnson bar, landing gear boots deteriorate. All these places can let the exhaust in during ground ops.

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That's not unusual depending on which way the breeze happens to be blowing.    Mine does this from time to time, enough that I no longer worry at all about what it's doing on the ground.   If it alarms on the ground I'll open the door or a vent just to keep myself from inhaling too much crap, but what matters is what it does in flight.    Even in flight there are certain configurations (e.g., landing, on my airplane), where it will read higher than in cruise.   I think you just need to get used to what is normal for your airplane.

 

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A lot depends on the wind direction...

until you have gained enough experience with both the plane and the sensor...

You kind of get stuck believing the sensor...

They are very sensitive devices...

7 on the ground is high but not unusual...

80 is time to find out what is going on... you might have somebody move the sensor around to see where The CO is coming in...  hard to do as a one man operation...

Putting it right in front of the heater air outlet... is a very telling location... A do not fly kind of thing...

Best regards,

-a-

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CO moves around so much,  so quickly, inside the cabin... it won’t make much of a difference where or how you mount it... for sensitivity...

Where you put it probably depends more on which alarm you want to perceive...

A visual alarm... up near the panel works pretty good...

an Audible alarm... up around your ears may be... alarming! :)

 

PP thoughts only, inviting Dan to stop in... @DanM20C

Best regards,

-a-

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10 hours ago, daytonabch04 said:

Where is the best place to put a CO reader in the plane?

I have 2 with audio warning: one near my head and one on the floor carpet near fuel switch, 

I hate to watch it all time as primary instrument, so now a glance once I think about fuel, heater, ap... does the job for me

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80 is not a worrisome reading in and by itself. If it's never been 80 before and now is 80 I would be concerned. But like others have said it could be wind direction etc. I would not hesitate to fly with this but monitor carefully while flying. I believe OSHA allows workers to work in an environment of 80ppm for 40 hours a week. So the number 80 is not what concerns me per se, it's that it has never been that high before...

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CO and the reason for CO is hard to figure, you can only know the conditions conducive to accumulation and monitor. I remember the original T-28 took down several pilots until it was discovered that flight with the canopy open created the problem. Close the canopy, no problem at all. I know some boats that in a strong wind will have CO collect below the swim platform with the generator set running, but in a calm wind, no problem. What is important is to have a monitor, when the readings go up understand the conditions that is causing it. I know for instance that if I open my storm vent window at low taxi speeds for whatever reason, CO starts accumulating. So under those conditions, I keep the vent closed.

 

 

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Thank you all for the advice!

Noted that it might be normal for it to read higher on the ground. However, I've had this carbon monoxide detector since I've had the plane, and it never read nearly enough to alert, so I was very suspicious of the sudden change.

Today I opened the cowl flaps and peaked under the right cowl flap, and here's what I saw (attached). Pretty sure it's not supposed to look like that.

An unfortunate design choice with this tube being routed so close to the cowl flap linkage :) Is this what you meant by a "scat tube going to the muffler" @M016576?

I've managed to find someone on-field to take a look at it on Tuesday. Hopefully they can patch or replace this tube and route it somewhere less in the way.

co.JPG

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Just now, Adi said:

Thank you all for the advice!

Noted that it might be normal for it to read higher on the ground. However, I've had this carbon monoxide detector since I've had the plane, and it never read nearly enough to alert, so I was very suspicious of the sudden change.

Today I opened the cowl flaps and peaked under the right cowl flap, and here's what I saw (attached). Pretty sure it's not supposed to look like that.

An unfortunate design choice with this tube being routed so close to the cowl flap linkage :) Is this what you meant by a "scat tube going to the muffler" @M016576?

I've managed to find someone on-field to take a look at it on Tuesday. Hopefully they can patch or replace this tube and route it somewhere less in the way.

co.JPG

Well that’s not what you want!

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Almost there...


glad you reported the 80 reading being not normal for your plane...  that is an indication of something changing recently...

That could be your CO source... Does the damaged hose look like recent damage? Like it tore this week...

To help Minimize any extra work.....  slap some tape on it. To block any air passing through the hole...

Go to the run-up area and see if you still get 80 on the CO meter...

You still get to fix this hose... probably better to just replace it to get a known working hose...

If you still get 80 on your CO meter... you get to fix the hose and still find the source of the CO.... :)

What is that hose attached to? (Look at both ends)

If that is the heater hose... it is still possible the heater is sending CO up through the middle of the hose... and the hole may have nothing to do with it...

CO is very serious... a small amount can turn into a deadly amount within the time of reaching altitude....  as in the source of the CO can increase remarkably... and unnoticeably.  Hard to understand the alarm under those conditions...

PP thoughts only, not  a mechanic...

Best regards,

-a-

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On 4/26/2020 at 7:57 AM, epsalant said:

80 is not a worrisome reading in and by itself. If it's never been 80 before and now is 80 I would be concerned. But like others have said it could be wind direction etc. I would not hesitate to fly with this but monitor carefully while flying. I believe OSHA allows workers to work in an environment of 80ppm for 40 hours a week. So the number 80 is not what concerns me per se, it's that it has never been that high before...

Sent from my Pixel 3 XL using Tapatalk
 

Actually, the OSHA PEL for CO is 50 ppm for 8 hr time weighted average. However, the ACGIH TWA is 25 ppm TWA, so I would consider 80 ppm a problem that needs correcting ASAP. I would not be surprised if 80 ppm exposure for an hour or so would cause a bad headache.

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10 minutes ago, MinneMooney said:

Actually, the OSHA PEL for CO is 50 ppm for 8 hr time weighted average. However, the ACGIH TWA is 25 ppm TWA, so I would consider 80 ppm a problem that needs correcting ASAP. I would not be surprised if 80 ppm exposure for an hour or so would cause a bad headache.

True.  I was speaking loosely.  50 is OSHA limit for 8 hour exposure. A minute or two at 80, I would think is VERY unlikely to cause any symptoms.  So if it was from the direction wind was blowing during run-up, not a problem.  If it doesn't go right back to low levels, then there's a problem.  If it happens again, there's a problem. 

CO is not something to be messed with.  I am NOT minimizing its importance.  It CAN be deadly.  I'm just saying one TRANSIENT reading of 80 is not necessarily an indication of a huge problem.  Definitely needs to be monitored.  If it returns to 0 and doesn't happen next run-up, it MAY have been wind blowing in exhaust.  Definitely needs to be monitored closely.

https://www.osha.gov/OshDoc/data_General_Facts/carbonmonoxide-factsheet.pdf

What are the OSHA standards for CO exposure?

  1. The OSHA PEL for CO is 50 parts per million (ppm). OSHA standards prohibit worker exposure to more than 50 parts of CO gas per million parts of air averaged during an 8-hour time period.
  2. The 8-hour PEL for CO in maritime operations is also 50 ppm. Maritime workers, however, must be removed from exposure if the CO concentration in the atmosphere exceeds 100 ppm. The peak CO level for employees engaged in Ro-Ro operations (roll-on roll-off operations during cargo loading and unloading) is 200 ppm.

 

 

https://www.kidde.com/home-safety/en/us/support/help-center/browse-articles/articles/what_are_the_carbon_monoxide_levels_that_will_sound_the_alarm_.html

Carbon Monoxide Levels and Their Symptoms

IMPORTANT: If your carbon monoxide alarm sounds, or you suspect you are experiencing symptoms of carbon monoxide poisoning, you should immediately leave your home and call 9-1-1.

 

50 PPM None for healthy adults. According to the Occupational Safety & Health Administration (OSHA), this is the maximum allowable concentration for continuous exposure for healthy adults in any eight-hour period.
200 PPM Slight headache, fatigue, dizziness, and nausea after two to three hours.
400 PPM Frontal headaches with one to two hours. Life threatening after three hours.
800 PPM Dizziness, nausea, and convulsions within 45 minutes. Unconsciousness within two hours. Death within two to three hours.
1,600 PPM Headache, dizziness and nausea within 20 minutes. Death within one hour.

 

NOTE: For more information about your specific alarm, refer to your user’s manual.

 

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On 4/26/2020 at 6:16 PM, Adi said:

 

Thank you all for the advice!

Noted that it might be normal for it to read higher on the ground. However, I've had this carbon monoxide detector since I've had the plane, and it never read nearly enough to alert, so I was very suspicious of the sudden change.

Today I opened the cowl flaps and peaked under the right cowl flap, and here's what I saw (attached). Pretty sure it's not supposed to look like that.

An unfortunate design choice with this tube being routed so close to the cowl flap linkage :) Is this what you meant by a "scat tube going to the muffler" @M016576?

 

That is EXACTLY what I meant!  I’m glad you looked that over and found it!  5’ of Scat tube costs about $25 from spruce (don’t bother patching it) and only takes about a half hour to replace... just sayin!

Edited by M016576
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The shop replaced the scat tube, rerouted it and also tightened a "loose joint on the exhaust".

I went to the run-up area today, got a reading of around 30-40.

I tried a bunch of things and they didn't seem to make much difference - revving up the engine for the runup, opening and closing the storm window, opening and closing vents/heat, moving the detector around the cabin. This time, though, opening the door caused an immediate drop in the reading. Also, I did notice that the reading stayed high when facing the wind or with the wind to the side, but were ~7 downwind. The readings were also low in the parking area where the wind is blocked by hangars.

The behavior does seem consistent with @N201MKTurbo's explanation above.

I didn't end up flying. I might try a quick flight tomorrow to see what it reads at altitude.

Edited by Adi
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Flying should have it settle with in seconds...

The exhaust coming out of the end of the tail pipe is a main source of CO while on the ground...

High angle of attack often supplies higher numbers by a few ppm... then cruise...

Cruise numbers should be near zero...

There are plenty of small leaks people have found where the exhaust sneaks back into the cabin from the back... see the bundle of wires back there... there should be material that plugs the airflow for that...

Best regards,

-a-

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Hey folks,

Flew the plane this morning. Readings of ~30 in the run-up area, 15 in climb, 3 in cruise. I thought the problem was solved :) (I forgot to check cabin heat in flight unfortunately)

However, when I tried to fly it in the evening just a few hours later, got a reading of >150 when going to 2000RPM for the run-up. Really sudden spike too - only took a few seconds to get there and it was still trending up when I abandoned the run-up. 

Back to the shop..

 

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31 minutes ago, Adi said:

Hey folks,

Flew the plane this morning. Readings of ~30 in the run-up area, 15 in climb, 3 in cruise. I thought the problem was solved :) (I forgot to check cabin heat in flight unfortunately)

However, when I tried to fly it in the evening just a few hours later, got a reading of >150 when going to 2000RPM for the run-up. Really sudden spike too - only took a few seconds to get there and it was still trending up when I abandoned the run-up. 

Back to the shop..

 

Ugh - well good thing for a fast responding digital CO monitor.  

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Congrats...

Sounds like the hole has opened up...

Expect this to be the heater... and CO is being delivered through the heat equipment...

There aren’t any other sources that have showed that much CO output to change in output...

It may help having a friend operate the CO meter... put it next to each air source in the cabin... each corner of the cabin...

Otherwise, you don’t want to be in a rush to guess where the CO is coming from...

Much better to find it then fix it...

No need to fly it.... Dan’s experience showed that the hole can open large enough to be unconscious in the climb... no need to repeat Dan’s experience...  once is enough...

Are you smelling the exhaust at all?

I used my CO meter in my car after getting some work done... it showed numbers near 100... and my clothes wreaked of exhaust after just a few minutes...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

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Nope, I didn't smell the exhaust at all. Yep, very glad I had the monitor, kind of want one for my car too now :).

 

Did Dan post about his experience on this forum? Would love to read about it.

I'll ask my mechanic to check for CO output throughout the cabin. All my flying friends are practicing social distancing so can't get much help unfortunately :)

For what it's worth, when I was moving the detector around, I didn't find any place that spiked.

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